1. Field of the Invention
The present invention relates to a sheet feed tray to have sheets placed thereon and an image forming apparatus to which this sheet feed tray is applied.
2. Description of the Background Art
There has been conventionally known a sheet feed tray to have a stack of sheets placed thereon in order to feed sheets to an image forming apparatus as disclosed in Japanese Unexamined Patent Publication No. H09-272635 (hereinafter, document 1) or Japanese Unexamined Patent Publication No. 2002-240964 (hereinafter, document 2). Such a sheet feed tray includes a pair of side fences opposed to each other in widthwise direction normal to the conveyance direction of sheets and extending in the conveyance direction, a pair of racks fixed to the corresponding side fences, extending in width direction and having toothed surfaces opposed to each other, and a pinion interposed between the respective racks in such a manner as to be engaged with the teeth of the respective racks.
In this construction, one side fence is moved in width direction, whereby this movement is transmitted to the other side fence via one rack, the pinion and the other rack, with the result that the other side fence is moved by the same amount in opposite direction. The pair of side fences needs to be accurately positioned relative to each other beforehand in order to feed sheets held therebetween to a specified position in the image forming apparatus in such a state as not to be displaced in sheet width direction.
Accordingly, in the sheet feed tray of document 1, the respective side fences are engaged with the pinion while being stopped by stoppers or outer stoppers transversely symmetrically disposed with respect to the pinion in order to be accurately positioned at the time of assembling the sheet feed tray. Thus, the respective side fences are accurately positioned relative to each other.
Contrary to this, in the sheet feed tray of document 2, positioning index are provided at one side of the pair of racks integral to the respective side fences and at one side of the pinion engaged with the respective racks, whereas applicable range marks corresponding to these index are provided on the other sides, and the index are caused to conform to the applicable range marks upon assembling the racks and the pinion into the sheet feed tray. Thus, the respective side fences are arranged at proper positions on the sheet feed tray.
However, in the sheet feed tray of document 1, the positional relationship of the side fences may deviate from the proper one since the side fences are merely stopped by the inner or outer stoppers.
Further, in the sheet feed tray of document 2, the positions of the index vary within a range defined by the applicable range marks even if the index are positioned within range defined by the applicable range marks. Therefore, there still exists a problem that the respective side fences cannot be accurately positioned.